Generally, a nuclear power plant (NPP) carries out a producing function of electric energy to be able to be used in practical living using nuclear energy by controlling a plenty of energy occurred by nuclear fission to be released slowly.
Here, though the possibility of occurrence is very low, corium of ultra-high temperature with radioactive feature may be released into a cavity of primary reactor containment under a nuclear reactor container by nuclear fuel of reactor core being molten and breakdown of nuclear reactor container when a severe accident occurs at a nuclear power plant. At this situation, the corium released is a radioactive material with ultra-high temperature higher than 2000K, and has a feature that heat is occurred endlessly. And when fail to cooling the released corium properly, the primary reactor containment of nuclear reactor constructed as a concrete structure may be damaged by the corium of ultra-high temperature and radioactive material may leak outside. In case that radioactive material being leaked from the primary reactor containment of nuclear reactor like this is released to soil or atmosphere, it may not only become a threat to a stability of the nuclear power plant facilities, of course become a pollution to the surrounding environment of the nuclear power plant, but also may cause a critical harmful influence to the health of ordinary general public.
Thus, recent nuclear power plant applies or develops a method for cooling and controlling properly the corium in the primary reactor containment of nuclear power plant in order not to leak the corium outside of the primary reactor containment of nuclear power plant. That is, a method of capable of cooling the corium with ease is required since the corium of high temperature released from a nuclear reactor container to a cavity pore of the primary reactor containment of nuclear power plant may melt and erode the floor concrete of the primary reactor containment of nuclear power plant if not cooled properly.
At this time, the cooling of released corium is divided upper portion cooling and lower portion cooling of the corium. Since a damage of floor concrete occurs by contact of lower portion of corium, a lower portion cooling of the corium is required. For this lower portion cooling of the corium, an indirect cooling method in which cooling is performed at a state a cooling-water and the corium are not in contact using a cooling container, a direct cooling method in which cooling is performed at a state a cooling-water and the corium are directly in contact, etc. may be applied.
Among this, the direct cooling method can get a more increased cooling efficiency than that of indirect cooling method since it cools directly the corium by contacting the corium and cooling-water, and has a merit of requiring less installation space. Thus, a development of a corium cooling apparatus is wanted with easy installation for application not only to a new nuclear power plant but also to a running nuclear power plant and capable of maximization of cooling efficiency.